Conduits, such as drill string, tubing, or casing are inserted into or pulled from oil and gas boreholes. During the insertion or removal process, the conduit may become stuck.
When the conduit is stuck, the operator determines the depth of the stuck point. Once the stuck point is determined, the conduit above the stuck point can be backed off or cut at a location just above the stuck point and the conduit is then removed.
To determine the stuck point, a tool is inserted into the conduit. The tool is commonly referred to as a free point tool; its role is to find the location just above the stuck portion of the conduit, referred to as the free point.
The free point tool is lowered to a depth and then coupled to the conduit by way of anchors. The anchors deploy out to engage the inside diameter of the conduit. In the prior art, the anchors are arms, the ends of which have serrations designed to contact a range of conduit inside diameters.
Once the anchors engage the inside diameter of the conduit, torsional and tensional deformations are applied to the conduit from the surface. The free point tool has sensors that measure the local torsional and tensional deformations downhole. Based upon comparison of these measurements to the applied loads, the free point of the stuck conduit can be determined.
With the prior art anchors, the anchors may slip and render the measurements inaccurate or suspect. This is because only part of the serrations contact the conduit inside surface. What is needed is an anchor that will hold more securely.